Как добавить сортируемую колонку в Joomla 3.4

Это мой код, но он не работает, скажите, пожалуйста, в чем моя проблема?
как добавить сортируемую таблицу столбцов в Joomla 3.x
Эта статья мне не помогла
Joomla добавление soratable столбцов

модель

class PwpModelPwp extends JModelLegacy {

private $perPage;
private $limitstart;
private $pagination;


public function __construct($config = array())
{
$config['filter_fields'] = array(
'nickname',
'country'
);
parent::__construct($config);
}

protected function populateState($ordering = null, $direction = null) {
parent::populateState('id', 'ASC');
}

public function listUsers(){
$db = JFactory::getDbo();

$this->perPage = 25;
$this->limitstart=JRequest::getInt('limitstart',0);

$query = $db->getQuery(true);
$query->select("*")
->from("#__pwpusers")
->setLimit($this->limitstart.','.$this->perPage)
->order($db->escape($this->getState('list.ordering', 'id')).' '.
$db->escape($this->getState('list.direction', 'DESC')));
$query = $db->setQuery($query);
$res = $db->loadObjectList();
return $res;
}
}

view.html.php

class PwpViewPwp extends JViewLegacy {
protected $items;
protected $state;
public function display($tpl=null) {

$items = $this->get('Items');
$state = $this->get('State');
$this->sortDirection = $state->get('list.direction');
$this->sortColumn = $state->get('list.ordering');
$task = JRequest::getVar('task');

switch($task) {

case "users":
$tpl = "users";
JToolBarHelper::addNew('pwp.addNew');
JToolBarHelper::custom('pwp.delUser', 'delete.png', 'delete_f2.png', 'Delete', false);
JToolBarHelper::back('Back');
break;
}
parent::display($tpl);
}

Вид / default.php

<?php
JHtml::_('behavior.formvalidation');
$model = $this->getModel('pwp');
$result = $model->listUsers();
?>
<script language="javascript" type="text/javascript">
function tableOrdering( order, dir, task )
{
var form = document.adminForm;

form.filter_order.value = order;
form.filter_order_Dir.value = dir;
document.adminForm.submit( task );
}
</script>
<form action="index.php?option=com_pwp&task=pwp.users" method="post" name="adminForm" id="adminForm" >
<table class="table table-striped" id="userList">
<thead>
<tr>
<td width="1"><input type="checkbox" name="toggle" value="" onclick="checkAll(<?=count( $result )?>);" /></td>
<th width="1"> # </th>
<th><?php echo JHTML::_( 'grid.sort', 'Nickname', 'nickname', $this->sortDirection, $this->sortColumn); ?>
<th><?php echo JHTML::_( 'grid.sort', 'Country', 'country', $this->sortDirection, $this->sortColumn); ?>
</tr>
</thead>
<tbody>
<?php
for($i=0;$i<count($result);$i++)
{
$row = $result[$i];
$checked    = JHTML::_('grid.id', $i, $row->id);

echo '
<tr class="row'.$i.'">
<td>'.$checked.'</td>
<td>'.$i.'</td>
<td><a href="'.JRoute::_('index.php?option=com_pwp&task=pwp.addUser&id='.$row->id.'').'">'.$row->nickname.'</a></td>
<td>'.$row->country.'</td>
</tr>';
}
?>
</tbody>
<tfoot>
<tr>
<td colspan="6"><?php echo $model->showPagination(); ?></td>
</tr>
</tfoot>
</table>
<input type="hidden" name="option" value="com_pwp" />
<input type="hidden" name="task" value="pwp.<?=$_REQUEST['task'];?>" />
<input type="hidden" name="filter_order" value="<?php echo $this->sortColumn; ?>" />
<input type="hidden" name="filter_order_Dir" value="<?php echo $this->sortDirection; ?>" />
</form>